1. Field of the Invention
The present invention relates to a data storage library of the type which has a plurality of independently rotatable data carrying sub-carousels which can be accessed by a linearly operated retrieval device.
2. Discussion of the Related Art
The carousel type of data storage library has become very popular because it is compact. Further, its data retrieval device, such as a cartridge picker, need only operate along one axis instead of two axes. The carousel library is especially useful for recordable media cartridges, such as cartridges for optical disks or cartridges for magnetic tapes or disks. The typical carousel rotates about a central vertical axis and has a plurality of cartridge receptacles which are arranged in vertical columns. The most compact carousel employs four columns arranged 90.degree. from one another about a common axis. This type of carousel takes up a minimum amount of floor space.
If a large library is needed in a small space, the four column carousel can be used by increasing its height. However, when the height is increased, the carousel becomes less efficient because of its increased weight. The designer attempts to keep the carousel as light as possible. However, when the carousel is filled with recordable media cartridges the total mass becomes substantial. This total mass is moved every time a new location is accessed by a cartridge picker. The results are slower access time and wear and tear on the motor and drive train.
An even greater problem of prior art carousel type data storage libraries is that when the motor and/or drive train fails the entire library is shut down. In the past there has been no provision for any backup operation of the library. A library could be shut down for literally days while waiting for proper servicing. This would be unacceptable to a user who relies upon the data in his library for the operation of his business.